Stereotactic body radiation therapy

(SBRT)

Dr Sadia Sadiq

PGR 2,INMOL

Historical Perspective

We should recognize and acknowledge that Stereotactic Body Radiation Therapy (SBRT) is an extension or evolution of Stereotactic Radiosurgery (SRS)

Why ?

If we acknowledge this evolution, we should also provide EXTRA-ORDINARY

CARE for SBRT as demanded in Stereotactic Radiosurgery (SRS)

Questions: Why is EXTRA-ORDINARYCARE necessary?

Why is EXTRA-ORDINARYCARE needed ?

Stereotactic body radiation therapy (SBRT)Management and delivery of image -guided high-dose radiation therapy with tumor-ablative intent within a course of treatment that does not exceed 5 fractions American Society of Therapeutic Radiology and Oncology (ASTRO)

Also called SART

Tumors include lung, liver, spine, pancreas, kidney, and prostate.

Prospective trials have demonstrated efficacy and acceptable acute and subacute toxicities

Late toxicity requires further careful assessment

Radiation: Fractionation

Standard fractionation: 1.8-2.0 Gy a day, 5 days a week for 25-30 treatments

Conventional hypofractionation:3-5 Gy a day, 5 days a week for 10-15 treatments

Stereotactic radiotherapy:15-25 Gy a day, 1-3 days a week for 1-5 treatments

Rationale of SBRT

Conceptual theories of cancer growth and numerous lines of evidence behind use of SBRT for metastatic lesions are

(a) The Empiric Or Phenomenological,

(B) The Patterns-of-failure Concept,

(C) The Theory Of Oligo metastases,

(D) A Lethal Burden Variation Of The Norton-simon Hypothesis, Or

(E) Immunological Enhancement.

Methods Of Cell Kill in SBRT

DNA damage

Anti Angiogenesis

Endothelial cell Apoptoses

1. Qualified personnel: a. Board-certified radiation oncologist b. Qualified medical physicist c. Licensed radiation therapist d. Other support staff as

indicated (dosimetrists, oncology

2. Ongoing machine quality assurance program; 3. Documentation in accordance with the ACR Practice Guideline

for Communication: Radiation Oncology;

4. Quality control of treatment accessories; 5. Quality control of planning and treatment images; 6. Quality control of treatment planning system; 7. Simulation and treatment systems based on actual measurement of organ motion and setup uncertainty.

SBRT PHYSICS AND TECHNOLOGY

1. CT simulation: Assess tumor motion

2. Immobilization: Minimize motion, breathing effects

3. Planning: Small field dosimetry considerations

4. Repositioning: High precision patient set-up: Fiducial systems, IR/LED Active and Passive markers, US, Video

5. Relocalization: Identify tumor location in the treatment field: * MV/ KV Xray, Implanted markers and/or set-up fiducials* Motion tracking and gating systems* Real-time tumor tracking systems with implanted markers

6. Treatment delivery techniques Adapted conventional systems Specialized SRT: Novalis, Cyberknife, Trilogy

4D CT Simulator

A technique that allow anevaluation of themotion of the targetFigure: Christopher Willey, MD, PhD

4D CT Simulator

The trace of the target motionallow the creation of ainternal target volume(ITV) for treatmentplanning

Stereo ImagingTechnology:

To localized the target on images On-Board Imager onLinac In-Room Localizer

Breathing-related motion control devices and systems fall into three general categories:

(a) dampening,

(b) gating, and

(c) tracking or “chasing.”

Respiratory dampening techniques Include systems of abdominal compression

intended to diminish one of the largest contributors to breathing-related motion, namely diaphragmatic excertion.

ABC:

Also included in this category are the systems employing breath-holding maneuvers to stabilize the tumor in a reproducible stage of the respiratory cycle (e.g., deep inspiration).

Gating systems for SBRT

It follow the respiratory cycle using a surrogate indicator for respiratory motion, for example, chest wall motion, and employ an electronic beam activation trigger allowing irradiation to occur only during a specified range of expected tumor locations.

Clinical Experience withStereotactic Body RadiationTherapy in Selected Sites

1)Lung2)Liver3)Spine4)Prostate5)Pancreas

SBRT:LUNG

Indications:

Stage I NSCLC

Pulmonary metastases

One important observation from the Indiana University studies was that although the treatment was generally well tolerated,

tumor location near large airways in the vicinity of the pulmonary hilum (called the zone of the proximal bronchial tree) was associated with a markedly higher risk of toxicity.

RTOG 0236:

•59 patients• Median age 72• All pts inoperable•T1 – 80%; T2- 20%•Dose: 60Gy in 3 fxs (BED 180)

Median FU 3 yrs:•Local control = 97.6%•Distant mets = 22.1%

•Overall survival @3yrs = 55.8%•Median survival = 48 months

Pulmonary metastases

SBRT: LIVER

Underlying severe liver disease often renders patients medically inoperable

Other nonsurgical therapies have generally achieved at best rather modest success in that setting.

Challenges in Targeting Liver TumorsLimited visualization of the targetLiver deformation with respiration Changes in GI organ luminal filling

Critical structures (stomach) may change in shape and position between planning and treatment

Interfraction target displacement with respect to bony anatomy

Abdominal Compression

Abdominal belt with inflatable bladder

Inflation: 15-40 mmHg

First Liver SBRT Experience 50 patients treated to 75 lesions with SBRT for primary and metastatic liver tumors

15 to 45 Gy, 1-5 fractions Mean follow-up of 12 months 30% of tumors demonstrated growth arrest, 40% were reduced in size, and 32% disappeared by imaging studies

4 local failures (5.3%) Mean survival time was 13.4 months

Blomgren, et. al., J Radiosurgery, 1998

SBRT:SPINE

SBRT is an emerging technology used for the treatment of spinal tumors.

Effective dose escalation For patients who are not candidates for conventional radiotherapy

To improve the quality of life for patients who may be spared a prolonged treatment course.

Acute Radiation toxicity is reduced.

Indications for Spinal SBRT

Pain control in vertebral metastases

Malignant Epidural Spinal Cord compression

Benign Spinal Cord Tumors

Dose volume constraints

In a Randomized trail of 260 patients investigators have not observed a single case of Myelopathy at 1 year with dose of 8Gy *1fr.

Partial volume tolerance of the human spinal cord to Radiosurgery was analyzed in 177 patients with 230 metastatic lesions.

The authors concluded that an acceptable estimate of partial cord tolerance is 10 Gy to the 10% volume.

1.Rades D, Stalpers LJ, Veninga T et al. J Clin Oncol 23:3366–3375

2.Ryu S, Jin JY, Jin R et al 2007Cancer 109:628–636

The a/b ratio of Prostrate Cancer is lower than for most other tumors. Values between 1.2 and 3 Gy are suggested.

It is lower than surrounding normal tissues like rectum (a/b of 4 Gy for late rectal sequelae).

It is hypothesized that hypofractionation if accurately delivered increases the tumor control by sparing surrounding late responding normal tissues.

SBRT:PROSTRATE

Indications

Primary treatment for organ confined low risk prostrate cancer

Dose escalation for intermediate and high risk prostrate cancer

prostate

SBRT: PANCREAS

Stereotactic body radiation therapy (SBRT) In Pancreas is indicated for

1.Boderline resectable tumors to improve resectability in Neo Adjuvuvant setting.

2.In Unresectable due to their lower life expectancy to reduce 5 -6 weeks treatment to less than 5 days

3.In resectecd Ca Pancreas with positive margins.

Challenges of SBRT in Pancreas

The head of the pancreas, where majority of tumors reside, is in close proximity to the C-loop of the duodenum

Delivery of conventionally fractionated radiation (1.8–2 Gy/day) to more than 50 Gy results in damage to the small bowel such as ulcerations, stenosis, bleeding, and perforation.

The pancreas move with respiration, as well as with peristalsis that is not easily predictable.

SIDE EFFECTS

Radiobiology: Tumor vs. Normal Tissue

Normal Tissue ToxicityLung: pneumonitis and fibrosisPancreas: duodenum and stomachSpine lesions: cordProstate: rectum and bladderLiver: normal liver (radiation induced liver disease-RILD)

The dose constraints of SBRT

Stereotactic Body Radiation Therapy:

The Report of AAPM Task Group 101

The SBRT:Ultimate “Targeted Therapy”